code: def test_null_graph(self):
      plt.close("all")
      g = Graph()
      fig, ax = plt.subplots()
      plot(g, target=ax)
      ax.set_aspect(1.0)
  
imports: import os
  import unittest
  from igraph import Graph, plot, VertexClustering, Layout
  from ...utils import overridden_configuration
label_desc: Use image node_id 14 for calling the GraphTestRunner obj's underlying member method code with example usage: obj.test_null_graph() without return types